1. Field of the Invention
The invention relates to the field of fireproof coverings for protecting heat-sensitive parts, and in particular, to protecting electrical cables, supporting means and the like in potentially dangerous environments such as found in petro-chemical plants.
2. Prior Art
Most electrical cables are now insulated with a plastics material. Most of the plastics materials used for cable coverings are heat-sensitive, readily flammable materials. Therefore, numerous proposals for making cables fireproof have been made. Thus, for example, it has been proposed to apply a self-quenching fireproofing agent to such cables, for example that known from German Pat. No. 2,039,969, corresponding to U.S. Pat. No. 3,642,531. However, this process is relatively complicated and costly, particularly in those cases where several juxtaposed cables must be protected against fire risks.
U.S. Pat. No. 4,064,359 discloses soft, flexible mats made of fiberglass, which possesses a relatively low heat resistance, for wrapping directly around pipes. By contrast, a coating on the flexible mat possesses a higher heat resistance. In other words, a coating containing high-melting fibers is used to compensate for the technically deficient fire-proof characteristics of fiberglass mats. The invention herein uses a similar coating, but in conjunction with rigid mineral wool panels made from hard, massive, relatively heavy, molded mineral fiber sheets. The fiber sheets are made of a hot-melting fiber material and have a much higher resistance to fire than fiberglass. The coating also improves resistance to chemical damage, impact damage and weatherproofing. However, the coating has yet another function, in that it sinters at temperatures between 700.degree. C. and 900.degree. C. (1290.degree. F. and 1650.degree. F.) and thereby provides a mechanical reinforcement of fiber structure at the surface of the mineral wool panels, the coating forming a substitute for the organic binder of the panels which decomposes when heated. Moreover, the sintered coating tends to be smoke-tight. Therefore, such a coating offers additional fire protection because it prevents or at least retards disintegration (dimmunition of volume, leaks at joints and a tendency to crumble) of the binding agent as it decomposes at temperatures above 300.degree. C. U.S. Pat. No. 4,064,359 mentions that the glass may be mixed with a suitable molding resin to form specific shapes. It also mentions that maximum fire protection properties are obtained when the inner layer is made up entirely of glass. Apart from this general statement, which is not further elaborated or supported, the disclosure does not contain even further hints regarding the mechanical and heat resistance properties of such molded fiberglass parts.
In German Utility Model No. 73 17 104 a panel element for sealing openings in walls and ceilings is disclosed. The panel elements are made of a fiber sheet, about 3 cm. to 6 cm. thick, made of mineral wool or glass fibers, and containing a resinous binder which vaporizes at about 200.degree. C. The panel elements are coated on both sides with a fire resistant coating. The composition of the coating can be compared with that of U.S. Pat. No. 4,064,359. No data is supplied in the Utility Model regarding the mechanical properties of the panel elements. The panel elements are not intended for forming channels for electrical ducts, but only for closing the openings.
A cable covering with a duct-like protective sheath has been proposed, which comprises two sheet steel layers, the gap between which is filled with mineral wool. However, in order to prevent corrosion in the construction of such protective sheaths, it is necessary to use stainless steel layers, or at least galvanized steel, which is expensive. In addition, metal protective sheaths require retaining devices as a result of their own weight. Such devices are relatively complicated and cannot always be properly fitted.